Synthesis of pyranopyrazole compounds using heterogeneous base catalyst based on 1,3,5-triazine-2,4,6-triamine modified nano rice husk silica

Many researchers have reported that rice husk is an excellent source of high-grade amorphous silica.Silica from rice husk offers a cheap alternative to commercial silica and at the same time help to solve rice husk disposal problem faced by rice milling industry [25]. A reaction between a carbon-halogen functional group and oneof the base organic compounds or ligands is anucleophilic substitution reaction.1,3,5-triazine-2,4,6-triamine (melamine), is a primary amine with three NH2 groups.These groups can be utilized for catalysis. We thought that the grafting of melamine onto the silica surface could afford a catalyst having a unique catalytic activity and selectivity due to the three NH2 groups. Pyranopyrazoles are important class of fused heterocyclic compounds, that are known for their wide range of biological activities such as fungicidal, bactericidal, vasodilatory activities [32] and they act as anticancer agents. There were few studies about the preparation of silica supported basic catalyst and its application for multi-component reactions (MCRs). herein, amorphous nanosilica was successfully extracted from rice husk (RH-SiO2), functionalized with melamine and used as a basic catalyst for the synthesis of pyranopyrazole compounds.Figure 1 shows the schematic representation of the synthetic pathway for RHA@Melamine solid base catalyst.